The coating before oxidation was 100 mm thick
and was composed of three zones: an outer layer of iron
aluminide, an aluminum-concentrated ferrite zone, and
an interdiffusion zone composed of alpha ferrite matrix
and nickel aluminide precipitates. It was confirmed from
a crude EDS analysis that the precipitates in the alpha
ferrite matrix were Ni3Al intermetallic phases. The outer
layer consists of FeAl intermetallic phase in this study,
but NiAl in the earlier study [13]. This may be attributed
to the difference in substrate composition and various
parameters of the coating process, although the parameters
were not reported in Ref. [13]